ECG INTERPRETATION:
the basics
Damrong Sukitpunyaroj,
Sukitpunyaroj MD
Perfect Heart Institue, Piyavate Hospital
Overview
• Conduction Pathways
• Systematic Interpretation
• Common abnormalities in Critical Care
– Supraventricular arrhythmias
– Ventricular
Ventric lar arrh
arrhythmias
thmias
Conduction Pathways
Conduction Pathways
P wave = atrial depolarisation.
PR Interval = impulse from atria
to ventricles.
ventricles
QRS complex = ventricular
depolarisation.
ST segment = isoelectric - part
of repolarisation.
T wave = usually same direction
as QRS - ventricular
repolarisation.
QT Interval = This interval
spans the onset of
depolarisation to the
completion of repolarization
of the ventricles.
ventricles
Interpretation
Interpretation
1.
Rate = Number of P’s (atrial) R’s (ventricular) per
minute (6 second [30 squares] X 10 = minute rate).
P rate: 8 x 10 = 80
2.
R rate: 8 x 10 = 80
Rhythm = Regular or irregular. Map P-P and R-R
intervals.
intervals
Interpretation
3 P wave = present,
3.
t 1 per QRS,
QRS shape,
h
d
duration,
ti
voltage.
lt
4. P-R interval = length (0.12 - 0.2 sec = <1 big square), isoelectric.
Interpretation
5. QRS = duration (0.06 - 0.10 ), voltage, q or Q waves
6. ST Segment = shape, isoelectric with PR segment
Interpretation
7. T wave = shape, direction
8. QT interval = length (R-R/2 or QTc <0.40 sec)
Abnormalities:
Supraventricular arrhythmias
• Atrial Fibrillation
• Atrial Flutter
• Supraventricular Tachycardia (SVT)
Abnormalities:
V t i l arrhythmias
Ventricular
h th i
• Premature Ventricular Complexes (PVCs)
• Ventricular tachycardia (VT)
Conduction Pathways
Supraventricular
Narrow QRS complex
Ventricular
V
ti l
Wide QRS complex
Abnormalities:
atrial fibrillation
Rhythm: Irregular
Rate: A: 350 – 650; V: varies
P: poorly defined
P-R: N/A
QRS: narrow complex
S-T: normal
T: normal
Q-T: normal
Abnormalities:
atrial flutter
Rhythm: Regular / Irregular
Rate: A: 220 – 430; V: <300 (2:1, 3:1 or sometimes 4:1)
P: Saw toothed appearance
P-R: N/A
QRS: narrow complex
S-T: normal
T: normal
Q-T: normal
Abnormalities:
supraventricular tachycardia (SVT)
Rhythm: Regular
Rate: >100
P: not visible
P-R: not defined
QRS: narrow complex
S-T: depression (sometimes)
T: normal
Q-T: prolonged (sometimes)
Abnormalities:
premature ventricular complexes
Examples
Examples
ECG INTERPRETATION:
12 Lead
Overview
• Lead Placement
• Axis
• Common abnormalities in Critical Care
– Heart block
– Bundle
B ndle branch blocks
– Life threatening arrhythmias
Lead Placement
V1 = 4th ICS right
i ht sternum
t
V2 = 4th ICS left sternum
V3 = midway between V2
and V4
V4 = 5th ICS midclavicular
V5 = between V4 and V6
anterior auxiliary line
V6 = midauxillary line
lateral to V4 and V5
Lead Placement
• Electrical activity towards = ↑
• Electrical activity away = ↓
Lead Placement
Axis
• The direction of an ECG
waveform in the frontal
plane measured in
degrees
• Represents
p
the flow of
the majority of electrical
activity
• Normally
N
ll the
h QRS
complex is measured
Axis
• Each lead has its own axis
Lead Placement
Standard Leads (bipolar)
• I - lateral wall
• II - inferior wall
• III - inferior wall
Augmented leads (unipolar)
• aVR - no mans land
• aVL - lateral wall
• aVF - inferior wall
Chestt L
Ch
Leads
d (unipolar)
• V1 - septal wall
• V2 - septal wall
• V3 - anterior wall
• V4 - anterior wall
• V5 - lateral wall
• V6 - lateral wall
Lead Placement
No-mans land, inferior, lateral, anterior, septal,
Abnormalities:
bundle branch blocks
• QRS widened, greater than 0.12 secs
• Change in axis
• Difficult to interpret ECG
• Right or Left
• Normal P wave
• Followed by a T wave
Abnormalities:
right bundle branch blocks
• Indicates conduction
problems in the right side of
the heart
• May be normal in healthy
people
• R wave in V1, ie two R waves
in V1
• Q wave in V6
• Lead V1 cats ears
Abnormalities:
left bundle branch blocks
• Always indicates heart
disease, usually of the left
side of the heart
• Hard to interpret an ECG with
LBBB
• Lead V1 Q wave and an S
wave
• Lead V6 an R wave followed
byy another R wave
• Lead V6 Rabbit ears
Abnormalities:
heart block
• SA block (exit block)
• 1st degree AV block
• 2nd degree AV block
– Wenckeback (type I)
– Mobitz
Mobit (type
(t pe II)
• 3rd degree AV block
Abnormalities:
heart block – SA block
Abnormalities:
heart block – 1st degree AV
Abnormalities:
heart block – 2nd degree AV
W k b k
Wenkeback
Mobitz
Abnormalities:
heart block – 3rd degree AV
Abnormalities:
life threatening arrhythmias
• Ventricular Tachycardia
• Ventricular Fibrillation
• Asystole
Abnormalities:
life threatening arrhythmias - VT
Abnormalities:
life threatening arrhythmias - VF
Abnormalities:
life threatening arrhythmias – Asystole
Examples
Examples